The effect of diet on the composition of chromatin from young and old rats

Abstract

The effect of diet on the RNA and protein content of chromatin from various tissues of young and old rats was investigated. It was found fasting 24–29 month-old rats for 48 hr caused a marked increase in the RNA content of chromatin in liver and kidney, while no such increase was observed in brain chromatin from rats of the same age or in any of the same three tissues from 3 to 5 month-old rats. When old rats which had been fasted for 48 hr were refed ad libitum for 6 hr, the chromatin RNA content dropped sharply, in every tissue. In young rats this drop was less prominent or nonexistent. Only slight changes in proteins were observed when rats from both age-groups were starved and refed. If, in the final step of the chromatin preparation, the salt concentration in the extraction solution or the extent of shearing during the extraction were varied, most of the protein was extracted together with DNA. In contrast, most of the RNA was extracted separately. More than one half of the RNA seems to be of small molecular weight as suggested by centrifugation in a sucrose gradient and dialysis.